Efforts to relieve the impending worldwide shortages of protein have included various biosynthesis processes wherein biologically produced single cell protein (SCP) is obtained by the growth of a variety of microorganisms on a variety of carbon-containing substrates.
The carbon and energy sources used as substrates for such processes should be available widely, relatively cheap, uniform, and safe in that they do not leave harmful residues in the proteinaceous product ultimately obtained by the microbial conversions. Petroleum hydrocarbons have been employed as the carbon and energy source material, but have faced practical difficulties in the lack of water solubility, in the high consumption of oxygen to assist in the microbial conversion, and allegedly in traces of potentially carcinogenic agents from the petroleum feedstocks entering or adhering to the protein product.
Other processes have used oxygenated hydrocarbon derivatives as feedstocks due to the water solubility of such derivatives and hence ease of handling since microbial conversion processes are essentially conducted under aqueous conditions. Such feedstocks are readily available either from petroleum sources, natural gas sources, various waste/garbage processing and conversion of methane, and the like, from fermentation of various grains and the like, destructive distillation of wood, and so on. Such oxygenated hydrocarbons, whatever their source, are widely available and relatively cheap feedstocks for fermentation processes. Advantages accrue in that these feedstocks are partially oxygenated, so that substantially reduced molecular oxygen requirements are involved for the microbial conversion-growth process itself.
However, another difficult and limiting factor in the commercialization of single cell protein processes has been the necessity to conduct the fermentation at relatively moderate temperatures of about 20.degree. to 50.degree. C., and preferably not over about 35.degree. C. Microbial conversions are exothermic oxidation reactions with large quantities of heat being produced. Heat must be removed from the fermentation admixture continuously and consistently, or risk the overheating of the system and either the death of the microorganisms or at least severe limitations of growth encountered as temperatures rise, and hence loss in efficiency.
Many processes have concentrated on the employment of one or other of the many available yeasts as the microorganism. Yeast cells generally are slightly larger than a bacteria cell, and sometimes provide easier separation from the fermentation process media.
However, bacteria offer advantages, since higher crude protein contents of the cell are obtained from bacteria as compared to the product obtainable from yeasts in general, since the yeasts have higher proportions of nonprotein structural material in their cells. Bacteria usually have a significantly higher true protein content, frequently being higher in the nutritionally important sulfur amino acids and lysine.
Discovery of bacteria with the capability of rapid growth and high productivity rates at relatively high fermentation process temperatures would be advantageous. High temperature growth operation means less heat to be removed, less cooling apparatus involved, and ultimately relatively smaller amounts of heat needed for sterilization, coagulation, and separation processes. Danger of contamination with other microorganisms is greatly reduced when high temperature fermentation can be employed. Thus, thermophilic or thermotolerant bacteria are definitely needed for commercialization of the single cell protein process.